The present invention relates to a semiconductor device having a substrate almost free from crystal defects and oxide film defects on the surface area thereof on which elements are formed, and a manufacturing method for the device.
FIG. 10 shows a substrate structure of a prior-art high-density integrated (i.e. ULSI) CMOS device. In the drawing, an island-shaped p-type well (diffusion region) 102 is formed on the surface area of an n-type semiconductor substrate 101 having a uniform resistance. Areas at which each element is formed are isolated from each other by a field oxide films 108. On the surface of the n-type semiconductor substrate 101, a gate oxide film 105 and a gate electrode G1 are formed, and, furthermore, a p.sup.+ -type impurity layer 103 is formed on both sides of the gate oxide 105 and connected to a drain electrode D1 and a source electrode S1, respectively, so that a P-channel MOS-type field effect transistor (referred to as P-channel MOS transistor, hereinafter) is constructed. On the other hand, on the surface of the p-type well 102, a gate oxide film 106 and a gate electrode G2, and a capacitor oxide film 107 and a capacitor electrode C are provided. In addition, an n.sup.+ -type impurity layer 104 is formed and connected to a source electrode S2 and a drain electrode D2, so that an N-channel MOS transistor and a capacitance are constructed.
With the advance of microminiaturization of semiconductor devices, however, there exists the tendency that crystal defects are introduced at pattern edge portions or gate oxide film defects (e.g. microdefects in gate oxide films) are introduced in MOS transistors. In case crystal defects exist at pattern edges, there arises problems in that junction leaks occur or the data holding time duration is shortened (in the case of a semiconductor memory device) or the production yield is reduced markedly. Furthermore, in case defects exist in a gate oxide film, malfunctions occur in the MOS transistor so that data cannot be held or the production yield is also reduced. The above-mentioned introduction of crystal defects is caused by supersaturated oxygen included in the silicon wafer in the form of solid solution. Therefore, it is necessary to reduce the oxygen concentration in the surface area of the substrate where elements are formed, in order to suppress the occurrence of crystal defects. That is, if the oxygen concentration is 3.times.10.sup.17 cm.sup.-3 or less, crystal defects and oxide film defects can be perfectly suppressed. On the other hand, as semiconductor substrates including supersaturation oxygen therewithin and having a 3.times.10.sup.17 cm.sup.-3 or less oxygen concentration at the surface area thereof, there exist an intrinsic gettering (IG) wafer, an epitaxial wafer, etc. In the case of the IG wafer, however, it is difficult to always maintain the oxygen concentration at 3.times.10.sup.17 cm.sup.-3 or less because the oxygen concentration is dependent upon treatment conditions and wafer properties. In the case of the epitaxial wafer, there exists another problem in that the substrate is polluted during epitaxial growth or the formed epitaxial layer includes defects. Accordingly, when micro-CMOS devices are manufactured by use of these wafers, there exists a problem in that junction leak occurs. As described above, conventionally, it has been difficult to reduce the oxygen concentration on the surface area of the substrate and to suppress the junction leak.